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Daily drug restores sight to hereditary blind

By Andy Coghlan

A hereditary form of blindness has been delayed or reversed for the first time by a daily drug treatment. The drug is the first to benefit people with a disease of their mitochondria, the energy powerhouses of cells.

There had been no way to halt the rapid onset of blindness in people with the most common mitochondrial disease, called Leber’s hereditary optic neuropathy. It strikes men in their twenties, leading to total blindness within three to six months of the first symptoms appearing.

But after receiving a drug called idebenone for six months, some people whose sight had begun to deteriorate reported drastic improvements in their vision that continued after the trial ended.

In the trial, 55 people received idebenone and 30 were given a placebo. After six months, 11 people who received idebenone could read an extra two lines on a standard vision chart – and nine people who could not read any letters at the outset could by the end.

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“This is not a cure, but it’s a significant effect,” says team leader Patrick Chinnery of Newcastle University in the UK.

Successful treatment

It is also the first time that an inherited mitochondrial disease has been successfully treated. “This trial tells us there’s hope for this and other mitochondrial diseases,” says Chinnery.

The drug didn’t work for everyone. The beneficiaries were those who, at the outset, had better vision in one eye than the other. Chinnery thinks this disparity means the disease is only just beginning to progress, and so is more treatable.

The disease strikes retinal ganglion cells that connect the light-sensitive cells of the retina to the brain via the optic nerve. Damage results from failure of mitochondrial enzymes to deliver electrons efficiently through the chain of reactions that generate energy. Idebenone is thought to deputise for these defective enzymes.

Chinnery says there were no serious side effects to the drug, and suggests that if carriers of the mutations can be identified through genetic testing, it might be possible to prevent blindness by giving the drug before symptoms develop.

He adds that it may be possible to use idebenone to treat other mitochondrial diseases. One possible candidate is Melas syndrome, a disorder resulting from defects in the ability of mitochondrial enzymes to clear lactic acid “waste” from cells, leading to brain swelling, heart and muscle weakness and a variety of other symptoms.

“It’s a great first step, and the suggestion that some patients benefit justifies further trials,” says Robin Ali of University College London, who is head of an ongoing gene therapy study in 12 people with Leber’s congenital amaurosis, a non-mitochondrial congenital form of childhood blindness.